The Washington database contains records of every fatal shooting in the United States by a police officer in the line of duty since Jan. 1, 2015.

In 2015, The Post began tracking more than a dozen details about each killing — including the race of the deceased, the circumstances of the shooting, whether the person was armed and whether the person was experiencing a mental-health crisis — by culling local news reports, law enforcement websites and social media, and by monitoring independent databases such as Killed by Police and Fatal Encounters. The Post conducted additional reporting in many cases.

The Post is documenting only those shootings in which a police officer, in the line of duty, shoots and kills a civilian — the circumstances that most closely parallel the 2014 killing of Michael Brown in Ferguson, Mo., which began the protest movement culminating in Black Lives Matter and an increased focus on police accountability nationwide. The Post is not tracking deaths of people in police custody, fatal shootings by off-duty officers or non-shooting deaths.

The FBI and the Centers for Disease Control and Prevention log fatal shootings by police, but officials acknowledge that their data is incomplete. Since 2015, The Post has documented more than twice as many fatal shootings by police as recorded on average annually.

The Post’s database is updated regularly as fatal shootings are reported and as facts emerge about individual cases. The Post seeks to make the database as comprehensive as possible. To provide information about fatal police shootings since Jan. 1, 2015, send us an email at policeshootingsfeedback@washpost.com.

The span between illegal gun purchase to criminal investigation has shortened every year since 2010. In just twelve weeks, one Glock 17 changed hands multiple times and was used to wreak havoc in Washington, D.C.